1. Field of Invention
The present invention relates to an operating frequency generating method and circuit for a switching voltage converter. More particularly, the present invention relates to an operating frequency generating method and circuit for a switching voltage converter capable of eliminating water wave, mura, flicker phenomena, etc. of liquid crystal display (LCD).
2. Description of Related Art
Among driving circuits of a display, for example a source driver and a gate driver of LCD, requires a switching voltage converter to generate the voltage required by the source driver and the gate driver. The switching voltage converters are mainly classified into two types, namely charge pump converters and pulse width modulation converters.
Generally speaking, the switching voltage converter must receive one clock signal serving as an operating frequency of its internal switch. The clock signal mainly comes from two sources: an independent voltage-controlled oscillator (VCO) and a certain digital period signal e.g. a dot clock signal, a horizontal synchronous signal, or a horizontal start pulse (or STH) signal in the driving circuit. The operating frequency of the switching voltage converter can directly adopt the clock signal coming from the above sources, or can be obtained by dividing the frequency of the signal coming from the above sources.
FIG. 1 is a clock diagram of a conventional switching voltage converter clock signal and a horizontal synchronous signal, vertical synchronous signal, and dot clock signal. In FIG. 1, Hsync represents the horizontal synchronous signal, Vsync represents the vertical synchronous signal, DOTCLK represents the dot clock signal, and CPCK represents the switching voltage converter clock signal.
When the switching voltage converter operates, the switching of the internal switch usually produces noises, which easily interferes the power supply voltage and other control signals of the driving circuit of display. As the operating frequency of the switching voltage converter and the control signal of the driving circuit have the visible timing correlation, many display defects e.g. water wave, mura, or flicker etc. are generated on the display.
Therefore, an operating frequency generating circuit and method for a switching voltage converter are required to solve the above problem.